I think you should do the following in order to get the newest version of Virtualbox OSE in the Debian repository:
Code:
apt-get update
apt-get install module-assistant
apt-get -t sid install virtualbox-ose
apt-get -t sid install virtualbox-ose-qt
apt-get -t sid install virtualbox-ose-source
m-a prepare
m-a a-i virtualbox-ose
There is a web page: VirtualBox OSE Debian install howto http://forums.virtualbox.org/viewtopic.php?f=7&t=26198